Original work done by Battelle (Battelle Memorial Institute) in the 1970s was directed to keeping root growth out of nuclear waste burial sites for a minimum expected life of 100 years. Battelle addressed the problem by developing buried pellets containing a herbicide (2,6-dinitroaniline) incorporated into a polymer (polyethylene) along with carbon black. The Battelle buried pellets, approximately 9 mm in diameter, were placed directly into the soil on a grid pattern at 2.5 to 5.0 cm spacing.
The work done by Battelle later resulted in issuance of U.S. Pat. Nos. 5,116,414 and 5,181,952 to Burton et al. Both of these patents disclose porous sheet materials having spaced apart bodies of a polymer containing 2,6 dinitroaniline for use as a root growth-inhibiting product; and both patents are incorporated in their entirety herein by this reference.
In the 1980s, Battelle's idea was followed by a development of geotextiles, particularly a non-woven fabric used as a carrier for pellets containing a herbicide. Pellets containing the herbicide trifluralin are spaced apart across the surface of the fabric, and when the fabric is buried in the ground, it affords protection against undesired root growth. One development which has been in use for many years is the geotextile fabric supplied by Fiberweb, Inc. which includes a pattern of nodules containing the herbicide trifluralin. That root barrier and weed control product is and has been sold under the registered mark Biobarrier, and is referred to herein as “the Biobarrier product.”
In the Biobarrier product, the presence of the trifluralin prevents root tip cell division; and when the Biobarrier material is used as a root barrier or for weed control, for example, the root systems of the weeds do not grow in adjacent areas into which the herbicide is dispersed.
In the Biobarrier product the nodules containing trifluralin applied to the fabric generally have a hemispherical shape, from which the herbicide can radiate directly outward into the soil during use. In one embodiment, the nodules have a radial dimension of about 9 mm, with a mutual spacing of about 4 cm. Each nodule radiates out a protective spherical dimension of about 3 mm, so each protects a sphere volume of about 14 cu cm. Assuming an area of 1 sq m, with nodules at 4 cm spacing, there are 625 nodules/sq m, or a zone of protection of 8,750 cu cm formed by the trifluralin moving in overlapping spheres directly away from the nodules.
The present invention is based on a recognition that the amount of herbicide used in the Biobarrier product, or similar products, is excessive, in fact wasted, given the amount of herbicide actually needed to provide a practical level of protection. This invention provides a much more efficient use of the herbicide material. Assuming the same 1 sq. m area of the fabric, for instance, an effective narrow zone of protection having a volume of 1,000 cu cm or less can be produced along the fabric by the present invention. This avoids the otherwise undesired wasteful prior art use of the herbicide. Advantages of the present invention include longer life of the herbicide and/or lower product cost for the same level of protection. Other improvements are also provided, as described in more detail below.